1. Field of the Invention
The present invention relates to a communication device in a VPN (Virtual Private Network) using an MPLS (Multi Protocol Label Switch).
2. Description of the Related Art
Generally, a scheme for an enterprise to configure a private network involves a method of configuring the network by using a private line, a method of configuring the network through a wide area LAN (Local Area Network) service using Ethernet VLAN (Ethernet Virtual Local Area Network), and a method of configuring the network based on a VPN (Virtual Private Network) using an MPLS (Multi Protocol Label Switch). In these methods, the method employing the MPLS is lower in cost and easier in operation management than the wide area LAN service, and therefore the VPN service using the MPLS is spreading.
The VPN service using the MPLS is exemplified by an IP-VPN (Internet Protocol Virtual Private Network) defined as the VPN service of a Layer 3, PW (Pseudo Wire) defined as the VPN service of a Layer 2 and as a Point-to-Point service, and a VPLS (Virtual Private LAN Service) defined as a Multipoint-to-Multipoint service. Any services involve using two labels such as an MPLS label (user identification label) for identifying user traffic and an MPLS label (tunnel label) for identifying a direction of the traffic.
The MPLS employs an LDP (Label Distribution Protocol) defined in RFC3036 as a protocol for dynamically distributing the labels in order to set up the MPLS tunnel. According to the LDP, the labels are distributed based on route information generated by a routing protocol such as OSPF (Open Shortest Path First). The route information contains a network address consisting of a set of a prefix and a prefix length of an IP (Internet Protocol) address, information on a next hop (next node), etc. The LDP gives a terminology of this network address referred to as an FEC (Forwarding Equivalent Class).
The LDP generates the MPLS tunnel according to the route information (the network address, the next hop information, etc) generated by the routing protocol such as the OSPF.
The OSPF involves frequently using route aggregation when operated in a multi-area environment. The route aggregation is a technique of aggregating plural pieces of consecutive route information in a certain area into one single route information and advertising this aggregate route information to another area. This technique has a merit that a routing table and topology information retained by each router can be reduced. The route aggregation is conducted normally by an ABR (Area Border Router) according to the OSPF.
Considered herein is a case of operating the LDP in an OSPF multi-area environment.
If the route aggregation is not conducted based on the OSPF, the network address in a certain area is advertised to other areas, respectively. Hence, the LDP enables the individual network address to be recognized as the FEC. With this scheme, the MPLS spanning between the areas per FEC can be generated.
FIG. 33 is a diagram showing an operation of the LDP if the route aggregation is not conducted based on the multi-area OSPF.
In FIG. 33, four nodes in an area 1 advertise loopback addresses of [1.1.1.0/32], [1.1.1.1/32], [1.1.1.2/32], [1.1.1.3/32], respectively. Further, the ABR connecting the area 0 and the area 1 to each other, in an OSPF process, advertises these four loopback addresses to the area 0 without performing the route aggregation. The OSPF on each of the nodes in the area 0 and the area 2 recognizes the four network addresses. The OSPF inserts the four network addresses as the FECs into the LDP, whereby the LDP can allocate labels to the respective FECs and can thus advertise the label-allocated FECs. As a result, the MPLS tunnels of the four FECs can be generated extending across the area 0, the area 1 and the area 2.
In FIG. 34, the four nodes in the area 1 advertise the loopback addresses of [1.1.1.0/32], [1.1.1.1/32], [1.1.1.2/32], [1.1.1.3/32], respectively. Further, the ABR connecting the area 0 and the area 1 to each other, in the OSPF process, route-aggregates these four loopback addresses into a network address of [1.1.1.0/30] and thus advertises this aggregate route address to the area 0. The OSPF on each of the nodes in the area 0 and the area 2 recognizes only this route-aggregated network address. This route-aggregated network address gets inserted as the FEC into the OSPF. The LDP can allocate the label to only the FEC defined as the route-aggregated network address and can advertise this FEC. As a result, the MPLS tunnels for the route-aggregated address are generated in the area 0 and the area 2. The MPLS tunnels for the route-aggregated address are terminated at the ABR that performs the route aggregation. The MPLS tunnels for the route-aggregated address are recognized as different tunnels from the individual MPLS tunnels within the area 1.
[Patent document 1] Japanese Patent Laid-Open Publication No. 2004-147021